Rubber composition and process of producing the same



Patented Mar. 1, 1932 p Y UNITED STATES PATENT oFncE No Drawing. Qrig inal application filed November 6,

,Serial No, 673,129. Divided and this application filed December 9,1929. Serial No. 412,915.

- This invention relates to'an improved rubber composition and method of producing the same; The invention particularly relates to a rubber composition having incorporated therein a materialsuch as that described in my co-pending application Serial N 0. 673,129, filed November 6, 1923, of which this application is a divisionah a-nd the method of producing the rubber composition.

Carbon ina very finely divided state, such as lamp black for example, is used for a variety of purposes, but difficulties often arise inhandling it because of its tendency to float in the air and settle up'on surrounding objects thus contaminating or blackening them. At.-

troduced together with the carbon into the place Where the same is to be utilized. Others have tried using agglutinants of different sorts, or binders for the carbon particles, so as to facilitate the introduction of the carbon particles into the places Where'they are to be used. a a I In accordance with the present invention, carbon is obtained in an exceedingly fine state of subdivision as soecalled free carbon? which is not chemically combined to any great extent with other elements, Without any danger Whatever of its flying aro'und atany time in the atmosphere and ruining adjacent objects by settling thereon. This invention does not require the provision of an expensive carrying medium for the-carbon but utilizes cheap materials that may be" readily obtained in large quantities. At the same time the carrying medium that is used can with safety be introduced together with the carbon par.- ticles Without injurious or deleterious results Where the carbon particles are needed or pere form their desired function. -o 1 It is Well known that tars contain so-called free carbon in amounts that vary with the source ofthe tars and the manner of productile constituents should ing the same. 1 Coal tars especially contain large amounts of free carbon varying considerably in tars from diiierent sources deventionutilizescoal tar as 1 which to obtain the product. In practicing this invention coal tar containing a high percarbon will be selected, or SQVGI'HldlflGIGIll? coal tars duiering in composition and percentages of free carbon sons to obtain a mixture contain ing a high percentage of free carbon, and this tar will be distilled toremove volatile constituents until a residue remains which contains40% or more by Weight of free carbon composed of carbon in a state of highly dispersed subdivision that is insoluble in benpounding. a

The distillation for the removal of the volabe carried on at such a temperature and for such a length of time that the residue Will contain no constituents that are volatile at the highest temperatures ordinarily used in rubber vulcanization. are used or when tars are so blended together as to make them adaptable for producing the desired product, the highest temperature required for the distillation step will be found to be in the neighborhood of 400 F., and the time required for the distillation will befound to be about ten to fifteen hours. While. the distillation is being carried on, great care must be exercised to keep the material in motion as by stirring or agitating the same mechanically or' in other suitable manner so as to prevent the same from beingburned or coked in spots will I (Lil ' not having the proportions of 50 and so as to maintain the same substantially homogeneous throughout. Such agitation while distilling seems to increase the amount of free carbon in the final product as wellv as to render it more suitable for rubber compounding. v

It has been found in actual practice that the residue produced as described above and containing large amounts of free carbon can be introduced into a rubber matrix orv mix and the carbon distributed throughout the same more evenly than is possible with other carbons and with less expenditure of time and power than are required carbons such as carbon blacks or lamp black. This case of introduction is probably due to the fact that the carbon is highly dispersed rial produced as described in this application the carbon is formed in situ in the hydrocarbon' medium as free carbonand does not have a tendency to flocculate but is susceptible of perfect dispersion in liquid'or plastic substances. The explanation for this is believed to reside in the fact that during the distillation each individual particle of carbon appears to become coated with a mineral wax which leavesthe particles free to disperse and overcome the tendency to flocculate.

As a p articular example illustrating the invention, I may start with a coal tar containing at least of free carbon or matter insoluble in hot benzol and toluol and I may distill the same for about twelve hours or until about or by weight of volatile matter has been removed, whereupon a resi-' due or pitch will be obtained which will contain at least 40% of free carbon as described above and have a melting, point of about 220 F. and specific gravity of about 1.3 and will be free from air and moisture and contains no appreciable amount of ashforming constituents. It is to be understood that tar having a highe percentage of free carbon than 20% may be usedto begin with or the distillation may be continued longer than indicated above, thus obtaining a finished product having a higher percentage of free carbon, but the example given has been found to proc uce a very satisfactory product to be used in rubber compounding. A prod parts by weight of free carbon to parts by weight of the mineral wax or material soluble in bowel has been found in actual practice to give very satisfactory results, when, for ex ample, automobile tires are to be produced,

although other proportions are also satisfacwith dry the raw material can,

tory, whereas, if rubber shoes, for example, are to be produced, a product with a smaller amount of free carbon can be used, and there are other products such as rubber soles, for example, in which a product with a larger amount of free carbon may be used with advantage.

Thev rubber and coal tar residue may be mixed together in any suitable manner and a product obtainedin which the highly dispersed carbon of the residue is mixed more evenly than is possible with other carbons such as lamp black or carbon black. The

proportions of the residue and the rubber em ployed in manufacturing rubber articles may vary considerably, depending upon the nature or characteristics of the rubber mix or w the rubber articles to be produced. Typical examples of theproportions of residue and rubber are as follows: In manufacturing tires from 10 to 15 parts by weight of the product described are combined with 100 parts by weight of rubber; in manufacturing rubber shoes from 3 to 7 parts by weight of the residue are employed for every 100 parts of total rubber including new rubber and reclaimed rubber; in manufacturing rubber soles the proportions may vary from 50 to parts by weight of residue to parts. of thetotal rubber content of the mixture.

If several tars are fblendedto obtain atar that is to be'distilled to produce the final roduct it is very desirable to mix the tars very thoroughly so as to obtain a uniform product to be distilled otherwisethe final product will not be as satisfactory. The blending of different tars to produce a suitable product to be distilled has been found to be desirable because of the difficulty of obtaining any one tar of suitable characteristics in sufficient quantities. A large supply of however, be obtaine by blending or mixing several tars from different sources.

The term free carbon as used in the specification and claims refers particularly, as hereinbefore indicated, to material insoluble in benzol, the amount of which present in the coal tar residue may be determined, for example, by themethod set forth on pages 7 36 and 820 (test D5) vol. 10 (1918) of the J our nal of Industrial & Engineering Chemistry.

'In'the appended claims where reference is made to benzol insoluble constituents of coal tar distillation residue which have been produced in situ,1 mean those constituents commonly known as free carbon which are present in coal tar or are formed in coal tar dis tillation residues during the reactions by which such residuesare produced as distinguished from free carbon otherwise formed.

I claim:

"1. A compositioncomprising rubber compounded. with a coal tar residue "containing Gil not less than about uents which have been produced in situ and which are insoluble in benzol, said residue having a. melting point of substantially 220 F.

2. A composition comprising rubber compounded with a coal tar residue containing not less than about 40% by weight of constituents which have been produced in situ and which are insoluble in benzol, said residue having a melting point not substantially over 220 F.

In Witness whereof, I have hereunto set my hand.

ARTHUR B. COVVDERY.

byeweight of constit- 

